Objective 1.1 – Tools and Summary

Well, that one objective dealt with. Just another 30 odd to go. Don’t forget that reading is not everything, you need to have done as much of this stuff as possible. There are links to VMware’s product documentation throughout, be sure to be familiar with it as the language and methods that they use there should be the same as you’ll find in the VCAP exam – I hope. … [Read more...]

Objective 1.1 – Analyse I/O Workloads

To put an application into a virtual environment you must first understand its I/O requirements to make sure that it will perform adequately on the storage that you have configured. This is very much like the process of determining how much CPU and Memory resource an application will need – it’s a necessary step. Of course you can miss it out and in the majority of cases that won’t be an issue but to keep your finger on capacity management  and to avoid possible problems it is best to follow a defined a repeatable set of steps. It’s also useful to be able to profile the I/O workload of applications already on a virtual platform. So, what do we need to know? Well although I have a fairly well-rounded set of skills, I am more of a … [Read more...]

Objective 1.1 – LUN Masking and PSA-related Commands

What is LUN masking? explains what LUN masking is in layman’s terms (in case you have a NAS only background). See Storage Masking? for the Yellow Bricks advice on LUN masking. For an overview of PSA and commands, see VMware vSphere 4.1 PSA. Also see the vSphere CLI guide, vSphere Command-Line Interface Installation and Reference Guide. … [Read more...]

Objective 1.1 – vCenter Storage Filters

From the ESX Configuration Guide. When you perform VMFS datastore management operations, vCenter Server uses default storage filters. The filters help you to avoid storage corruption by retrieving only the storage devices, or LUNs, that can be used for a particular operation. Unsuitable LUNs are not displayed for selection. You can turn off the filters to view all LUNs. Before making any changes to the LUN filters, consult with the VMware support team. You can turn off the filters only if you have other methods to prevent LUN corruption. Procedure In the vSphere Client, select Administration > vCenter Server Settings. In the settings list, select Advanced Settings. In the Key text box, type a … [Read more...]

Objective 1.1 – Raw Device Mapping (RDM)

Read Performance Characterization of VMFS and RDM Using a SAN. It may be for ESX 3.5 but still holds true. The conclusion from the document is: VMware ESX Server offers two options for disk access management—VMFS and RDM. Both options provide clustered file system features such as user‐friendly persistent names, distributed file locking, and file permissions. Both VMFS and RDM allow you to migrate a virtual machine using VMotion. This study compares the performance characteristics of both options and finds only minor differences in performance. For random workloads, VMFS and RDM produce similar I/O throughput. For sequential workloads with small I/O block sizes, RDM provides a small increase in throughput compared to VMFS. … [Read more...]

Objective 1.1 – VMware Storage Best Practices

Obviously the choice of storage vendor and the underlying technologies play a part here but there are some general guidelines that apply regardless. VMware themselves have a short page on this which I have copied below: Many of the best practices for physical storage environments also apply to virtual storage environments. It is best to keep in mind the following rules of thumb when configuring your virtual storage infrastructure: Configure and size storage resources for optimal I/O performance first, then for storage capacity. This means that you should consider throughput capability and not just capacity. Imagine a very large parking lot with only one lane of traffic for an exit. Regardless of capacity, throughput is affected. … [Read more...]

Objective 1.1 – RAID levels for VM workloads

There isn’t a single rule for this – there are more like thousands of rules! Basically have an idea of what workloads VMs are generating in terms of IO and try to balance them out but also bear in mind that write intensive loads will perform better on RAID 10 than on RAID 5 but RAID 10 uses more disks than RAID 5 does. Whilst not specifically related to RAID and it talks about EMC storage, Optimal VM Placement offers some interesting thoughts and mentions the alarms that can be set in vCenter that are usueful to monitor problems: VM Disk Usage (KBps) Total Disk Latency (ms) VM Disk Abort VM Disk resets Also, as a rule of thumb, if a server consistently generates a certain number of IOPS as either reads or writes on … [Read more...]

Objective 1.1 – NPIV

From How NPIV-Based LUN Access Works: SAN objects, such as switches, HBAs, storage devices, or virtual machines can be assigned World Wide Name (WWN) identifiers. WWNs uniquely identify such objects in the Fibre Channel fabric. When virtual machines have WWN assignments, they use them for all RDM traffic, so the LUNs pointed to by any of the RDMs on the virtual machine must not be masked against its WWNs. When virtual machines do not have WWN assignments, they access storage LUNs with the WWNs of their host’s physical HBAs. By using NPIV, however, a SAN administrator can monitor and route storage access on a per virtual machine basis. The following section describes how this works. NPIV enables a single FC HBA port to … [Read more...]

Objective 1.1 – VMware DirectPath I/O

DirectPath places some limitations on VMs and so is used with caution. Generally, any VM that uses DirectPath becomes tied to an ESX host - vMotion and DRS will not work. DirectPath must first be enabled in the ESX host's BIOS. As a consequence only certain systems support this. A PCI device can only be assigned to 1 VM at a time. That device cannot also be used by the host. A VM can have upto 2 directly connected devices. The advantage that DirectPath gives is the ability for devices not directly supported by VMware to be attached to VMs. Also, by circumventing the virtualisation layer, greater performance can be achieved by a VM using a directly connected device. Typically DirectPath is used to assign high speed, dedicated … [Read more...]